J OURNAL OF FOREST PRODUCTS & INDUSTRIES, 2014, 3(3), 151-153 ISSN:2325–4513( PRINT) ISSN 2325 - 453X (ONLINE )
Research Article 151
Properties of Poly(vinyl alcohol) Plasticized by Glycerin
Jia Pu-you1, Bo Cai-ying1 , Hu Li-hong1，2, Zhou Yong-hong1*
1
Institute of Chemical Industry of Forest Products, CAF; National Engineering Lab. for Biomass
Chemical Utilization; Key and Open Lab. on Forest Chemical Engineering, SFA; Key Lab. Biomass Energy and
Material, Jiangsu Province, Nanjing 210042, China
2
Institute of New Technology of Forestry, CAF, Beijing 100091, China
(Received: April 04, 2014; Accepted: May 19, 2014)

Abstract— The plasticized poly(vinyl alcohol) (PVA) films were
prepared by the casting method using glycerin as the plasticizer.
The interaction between PVA and glycerin was analyzed by
Fourier
transform
infrared(FTIR)
spectroscopy,
Thermogravimetric analysis(TGA) and Differential scanning
calorimetry(DSC). Thermal properties, water resistance and
mechanical properties of PVA and plasticized PVA were studied
respectively. It was found that the glass transition temperature
and thermal decomposition temperature of modified PVA were
lower than PVA. The plasticized PVA had lower strength and
higher elongation at break, lower degree of swelling and higher
solubility than PVA.
Index Terms — Poly(vinyl alcohol); Glycerin; Plasticizers;
Modified
I. INTRODUCTION
P
oly(vinyl alcohol)(PVA) has excellent film forming,
water-soluble, adhesion, emulsification and barrier
properties, which has been used in fibers, films and adhesive
agents widely[1-4]. The structure of PVA molecule has many
hydroxyl groups, which can form hydrogen bonds, this
hydrogen bonding gives PVA many excellent properties. But
the PVA film has the defects of low elongation at break, poor
decomposition temperature and high glass transition
temperature. The defects affect the application of PVA widely.
So PVA was studied by many researchers. Jiang X C[5-7]
studied the PVA which were prepared through the melt
processing by employing magnesium chloride and
polyethylene glycol as the complex plasticizer, the results
showed that the plasticizer can effectively destroy the hydrogen
bonding between PVA molecules and decrease the crystallinity
and melting point of PVA significantly. Then he used MgCl2 as
plasticizer of PVA, the results showed that the modified PVA
was with lower tensile strength and higher elongation at break
than PVA. Ren D C [8] used urea/triethanolamine as a mixed
plasticizer to modify PVA, he found that with the mass fraction
of mixture of plasticizer increasing, the modified PVA was
with lower tensile strength and higher elongation at break, good
light transmission rate, lower degree of swelling and higher
solubility than pure PVA. Jiang T [9] studied the plasticized
starch/PVA films which were prepared by casting method
using magnesium nitrate as the plasticizer. It was found that
magnesium nitrate could form some interaction with starch and
PVA molecules, magnesium nitrate could destroy the crystals
*Corresponding author E mail: [email protected]
of starch. Tensile testing showed that magnesium nitrate was
highly effective in modifying the mechanical properties of
starch/PVA films. In summary, the thermal properties and
mechanical properties of plasticized PVA were improved by
destroying the hydrogen bonds of PVA molecular. In this
paper, we use glycerol as the plasticizer to improve the thermal
properties and mechanical properties of PVA.
II. MATERIALS AND METHODS
Materials
PVA (AR) was purchased from ShangHai Yingjia Industrial
Development Co., Ltd. (Shanghai, China). The degree of
polymerization is 2400. Glycerin was purchased from NanJing
Chemical Reagent Co., Ltd. (Nanjing, China) [5-6].
Samples preparation
3g PVA and 1.2g PVA was dissolved in distilled water by
heating in an oil bath at 95℃ for 2h. Then the solution was
casted into a clean glass Petri dish (diameter 12cm) and dried at
60℃in the vacuum oven to completely eliminate water. Then
the dried films were stored at RH of 54% for one week before
testing. Films without plasticizer addition were also prepared as
control [5-6].
Testing and characterizaton
The FTIR studies were carried out using a IS10 (PE Company,
USA). The spectra were acquired in the range of 4000-400 cm-1
at a resolution of 4 cm-1
Glass transition temperature (Tg) was determined by
differential scanning calorimetry using a Diamond DSC (PE
Company, USA). Samples od about 7mg were condition in
aluminum pans and heated at 20k/min under an inert
atmosphere of N2(50ml/min N2 ) between 40-600℃. An empty
pan was used as reference.
Thermogravimetric analysis was carried out in a TG209F1
(Netzsch Company,Germany) in N 2 atmosphere(50ml/min) at
a heating rate of 20k/min. The samples were kept into platinum
and scanned from ambient temperature to 600℃.
PVC films and plasticized PVA films after drying and weighing
were put in deionized water for 24h, then weighed the samples
after drying with filter paper. The calculation formula of
swelling ratio is DS=(We-Wo)/ Wo, We: the mass of PVA
films after swelling balance; Wo: the dry weight of PVA films.
The samples were weighted after swelling balance were put in
vacuum oven at 60℃ for 24h. The calculation formula of
152
J OURNAL OF FOREST PRODUCTS & INDUSTRIES, 2014, 3(3), 151-153 ISSN:2325–4513( PRINT) ISSN 2325 - 453X (ONLINE )
dissolution rate is S=（Wo-Wd）/Wo, Wd: the dry weight of of
PVA films after swelling balance.
Tensile strength and percentage tensile elongation at break of
the films were determined at room temperature using an Instron
5567
mechanical
property
measurement
following
GB13022-91, the Chinese standard equivalent to ISO 527-4.
Differential scanning calorimetry
Differential scanning calorimetry was performed in order to
determine the glass transition temperature (Tg) of polymeric
matrix. The temperature is an important parmeter in polymer
characterization being able to evaluate the plasticizing effects
of substance added to polymeric systems.
III. RESULTS AND DISCUSSION
DSC curves of PVA and plasticized PVA are shown in Fig.2.
The addition of the glycerol to PVA film shifted the Tg towards
lower temperature, from 348.5℃ in the PVA film to 328.5℃ in
the plasticized PVA. The PVA has a large number of hydrogen
bonding, which makes PVA a stable state of aggregation and
high degree of crystalline, so the PVA has a high glass
transition temperature. The addition of glycerol destroyed the
hydrogen bonding, the activity of PVA chains will be
enhanced, which reduced the glass transition temperature.
The FTIR measurements
There are many hydroxyl groups on PVA chains and they can
form hydrogen bonding easily. The crystalline, thermal and
mechanical properties of PVA can be affected by the intensity
of the hydrogen bonding in PVA. The recent studies showed
that the intensity of the interaction between the plasticizer and
PVA is critical for the plasticizing efficiency of the plasticizer.
It is a efficiency way to study the hydrogen bonding for in the
infrared region using FTIR, the vibrations of molecules can be
investigated. The pure PVA and PVA plasticized with the
Glycerin were obtained and shown in Fig. 1. There is no
absorption band of free “-OH” at 3600cm-1 for PVA. This
indicates the hydroxyl groups are generally associate with the
intermolecular and intramolecular hydrogen bonding. It was
shown in Fig.1 that the absorption band of “-OH” shift to a
higher wave number after the addition of the complex
plasticizer of Glycerin. The shift in the frequency is valuable as
the measurement of the hydrogen bonding of the hydroxyl
group. It indicates that the hydrogen banding is weakened when
the frequency shifts to a higher value. From the Fig.1, the
spectrum of pure PVA showed the absorption of hydroxyl at
3255.15cm-1, the absorption band of hydroxyl shifted to a
higher value at 3271.96cm-1 with the addition of the complex
plasticizer (PVA-P), it indicated that the addition of the
Glycerin would reduce the intensity of the hydrogen of bonding
of PVA molecules. It is because Glycerin forms strong
hydrogen bonding with PVA, which take place of the hydrogen
bonding between the hydroxyl group of PVA molecules.
Glycerin reduces the intensity of the hydrogen bonding in PVA,
it showed that Glycerin have a plasticizing effect for PVA.
Fig.1 IR Spectra of PVA and modified PVA
Fig.2 DSC curves of PVA and modified PVA
Thermogravimetric analysis
Thermogravimetric curves of PVA and plasticized PVA were
showed in Fig 3. We can get the decomposition temperature
from the thermogravimetric curves. International Bureau of
standards (ISO) defined the temperature of intersection which
was between the base line and the extended line of the
connection of 20% weight loss and 50% weight loss point as
the decomposition. In the thermogravimetric curves of PVA
and plasticized PVA, the point A,B and C, D is 20%weight loss
and 50% weight loss point of PVA and plasticized PVA
respectively. The point E and F is the decomposition of PVA
and plasticized PVA respectively, it is 218℃and 227℃.
Because plasticized PVA contains many small molecules, they
will volatile when the temperature from 100℃ to 600℃, the
thermogravimetric curves of PVA is lower than the PVA.
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J OURNAL OF FOREST PRODUCTS & INDUSTRIES, 2014, 3(3), 151-153 ISSN:2325–4513( PRINT) ISSN 2325 - 453X (ONLINE )
IV. CONCLUSION
The Glycerin was proved to be with a high plasticizing effect
for PVA by all the results in our article. Glycerin could interact
with PVA molecules and replace the hydrogen bonding within
PVA molecules. The crystallization of PVA was interrupted
and the intensity of the hydrogen bonding in PVA was reduced
in the way. The Glycerin could improve the compatibility of
PVA, and the plasticized PVA films appeared a more
continuous than pure PVA films. The thermal stability and the
glass transition temperature of decreased with the addition of
Glycerin. The mechanical properties of PVA were improved
significantly and the plasticized PVA films appeared a more
tougher than pure PVA films after adding the Glycerin. It can
also be expected that the Glycerin could play an important role
in the polymer such as cellulose that contains many hydroxyl
groups.
Fig.3 TG curves of PVA and modified PVA
Swelling ratio and dissolution rate
The value of swelling ratio and dissolution rate are showed in
Table 1. From table 1 we can see that the degree of swelling
PVA and modified PVA is 2.62 and 1.76, the solubility is 0.24
and 0.39 respectively. The reason why the modified PVA has
lower degree of swelling and higher solubility is that hydroxyl
of PVA has been destroyed.
Mechanical properties
The value of mechanical properties of PVA and modified PVA
films are showed in Table1. The elongation at break of PVA
and modified PVA is 210.58% and 360.20% respectively. The
tensile strength of PVA and modified PVA is 32.26 MPa and
17.12MPa respectively. We interpreted that the change of
mechanical properties arises from the degree of the
crystallinity. The entanglement and interaction between PVA
chains was weak and then the tensile strength decreased when
the PVA was with a lower crystallinity. Because the plasticizer
was with higher plasticizing efficiency, PVA would be more
completely melted to form a continuous phase and thus show
better mechanical properties.
Table 1
Swelling ratio, dissolution rate and mechanical
performance parameters
PVA
PVA(40%)
Degree of swelling 2.62
1.76
Solubility
0.24
0.39
Elongation at
210.58
360.20
break(%)
Tensile
32.26
17.12
strength(MPa)
REFERENCES
[1]Yan R X. Water-soluble polymer[M].Beijing, Chemical
Industry Press, 1998,42-43
[2]Zhao L, Tang G W, Su J F, etal. Electrospinning of soy
proten isolate/poly(vinyl alcohol)[J]. Chem.J.Chinese
Univeraities, 2010,31（4）:811-814
[3]Wang X L, Zhang Y R, Wang Y Z. Recent progress in
starch-based polymeric materials[J]. Acta Polymerica
Sinica, 2011,1（1）:24-37
[4]Ma H H, Shi T J. Morphology and property of
PVA/SiO2-TiO2
hybrid
electrospun
fibers[J].
Chem.J.Chinese Univeraities, 2009,30（9）：1885-1890
[5]Jiang X C, Xu W P, Tang Y D, etal. Studies on properties
of
PVA
film
plasticized
with
mixture
of
urea/ethanolamine[J].
Acta
Polymerica
Sinica,
2010.9:1144-1147
[6]Jiang X C, Xia Z, Ye D Z, etal. Properties of poly(vinyl
alcohol) plasticized by magnesium chloride[J].
Chem.J.Chinese Univeraities, 2012,33（8）:1872-1876
[7]Jiang X C, Song J, Jing T, etal. Melt processing of PVA
with magnesium Chloride and polyethylene glycol as the
complex plasticizer[J]. Chem.J.Chinese Univeraities,
2013,34(10):2451-2456
[8]Ren D C, lin P, Qin L, etal. Effect of mixture of plasticizer
on properties of PVA films[J].Journal of materials
engineering, 2012.6:87-90
[9]Jiang T, Jiang X C, Zhang X F, etal. Preparation and
properties of starch/poly(vinyl alcohol) film plasticized by
magnesium nitrate haxahydrate[J]. Chem.J.Chinese
Univeraities, 2012.33（12）:2282-2826